A pair of recent European studies yielded somewhat mixed evidence on the benefits of pneumococcal vaccines, with the 13-valent vaccine for young children appearing more effective than the 23-valent vaccine for older adults.

Writing in Clinical Infectious Diseases, French researchers reported that use of the 13-valent (13-strain) pneumococcal conjugate (PCV13) vaccine was linked to a significant reduction in community-acquired pneumonia (CAP) in children after it replaced the 7-valent PCV in France in 2010.

In the same journal, Spanish investigators said that receipt of a 23-valent pneumococcal polysaccharide vaccine (PPV23) did not appear to reduce CAP incidence in adults older than 60 overall, but vaccination within the past 5 years did appear beneficial.

Pneumococcal vaccines target Streptococcus pneumoniae, which causes a major share of pneumonia cases as well as infections of the blood, middle ear, and meninges. PCV13 is used in children under age 5, while PPV23 is recommended for older adults.

PCV13 findings

To examine the impact of PCV13 on CAP, the French team prospectively monitored radiography-confirmed pneumonia cases in eight pediatric emergency departments before and after the vaccine was introduced (from June 2009 to May 2012). Children from 1 month to 15 years old were included.

The team counted 5,645 CAP cases, which included 365 cases of CAP with pleural effusion and 136 cases of documented pneumococcal CAP. Overall, CAP cases dropped by 16%, from (2,060 to 1,725) between the before and after periods. The decrease was a significant 32% (from 757 to 516) for children under age 2.

The researchers also found that the number of pleural effusion cases declined by 53% (167 to 79) and the count of pneumococcal CAP cases sank by 63% (from 64 to 24). Both decreases were significant.

The findings were welcomed in an accompanying commentary by Keith P. Klugman, MD, PhD, of the Bill & Melinda Gates Foundation.

"The data suggest herd protection in children 2-5 years of age who were not vaccinated," he wrote. "This would be a very quick herd effect given the lack of catch-up [vaccinations in children older than 5], but it is biologically plausible given the high rates of vaccination among children less than 2 years of age."

Klugman added that the study has limitations in that it is an observational study with no control group, "but the excellent microbiology and serotype-specific reductions in the invasive disease surveillance are indicative of a causal effect." He also cautioned that the pre-PCV13 year was the year of the 2009 H1N1 influenza pandemic, so the reductions in CAP seen after the vaccine's introduction may have been affected by a high baseline and by reduced flu activity in the ensuing years.

PPV23 study

The Spanish researchers examined the effects of PPV23 by prospectively counting pneumococcal and all-cause CAP cases in people over age 60 in Tarragona, Spain, for 3 years, from December 2008 through November 2011.

The study cohort consisted of 27,204 people who were followed for 76,033 person-years, including 29,065 person-years for vaccinated individuals. "In primary analyses including all cohort members, the vaccine did not appear to be effective against any analyzed outcome," the report says.

But when the authors compared those who had received PPV23 within the past 5 years to those never vaccinated, they found that the recent vaccinees had a 51% lower risk of pneumococcal CAP (hazard ratio, 0.49; 95% confidence interval [CI], .29 to .84) and a 25% lower risk of all-cause CAP (hazard ratio, 0.75; 95% CI, .58 to .98).

"Our data support a protective effect of recent PPV23 vaccination (within previous 5 years) against both pneumococcal and all-cause CAP," they write.

Commenting on this study, Klugman wrote, "These data are hard to interpret because there were so many differences in risk factors between those immunized and unimmunized (including a massive difference in influenza immunization)." But he added that examining PPV effectiveness according to time since vaccination makes sense because the vaccine is "T-cell independent and lacks a mechanism for long-term boosting of the immune response."

Klugman said the study indicates that the vaccine provides "at best limited protection in a subset of vaccinees for less than 5 years." He went on to assert that for the long term, conjugate vaccines need to become the primary tools for preventing pneumococcal pneumonia.

"The study from Spain, in its most optimistic interpretation, does not suggest that we can rely on unconjugated polysaccharides for long-term immunity," he said. "The days of such unconjugated polysaccharide vaccines as a public health tool to reduce the burden of pneumococcal pneumonia in populations are, in my view, numbered, and their utility is confined to individual protection for some at-risk populations."